1. Field of the Invention
The present invention generally relates to thermal-recording labels, and particularly relates to a thermal-recording label which has a thermal coloring layer on one side of a supporting sheet and a thermal adhesive layer on the other side, which adhesive layer is non-adhesive before activation and includes an infrared absorption substance.
2. Description of the Prior Art
Thermal-recording labels are widely used in various fields including the field of POS (point of sales) systems, and typically have a peeling sheet attached on an adhesive layer on the back surface thereof.
Although thermal-recording labels of a self-adhesive type as described above are effective for their intended purposes, there are various disadvantages associated with the peeling sheets, which are typically larger than the labels themselves. For example, an amount of a limited capacity of storage must be used for storing those large non-essential sheets, which are to be disposed of after using the labels. Also, those large sheets hinder to some extent work performance during sticking of the labels. Also, disposing of those large sheets after the sticking of the labels is not preferable from an ecological viewpoint. Furthermore, a cost of attaching the peeling sheets as well as a cost of the peeling sheets themselves adds to a cost of the thermal-recording labels.
In order to obviate the problems described above, self-adhesive thermal-recording labels without peeling sheets are disclosed in Japanese Laid-Open Utility Model Application No. 59-43979 and in Japanese Laid-Open Patent Applications No. 59-46265, and No. 60-54842. Those disclosures describe thermal-recording labels with an adhesive encapsulated in micro-capsules, thermal-recording labels with a detaching-agent layer for an adhesive provided on a protective layer, etc. However, the thermal-recording labels disclosed in those patent applications have defects such as a week tackiness of adhesives and a difficulty in printing on the thermal surface, and, thus, are not applied in practical use yet.
A method of using a thermal adhesive as a functional adhesive is disclosed in Japanese Laid-Open Patent Application No. 63-303387 and Japanese Laid-Open Utility Model Application No. 5-11573. Both of them use a foaming heat insulator or a non-foaming heat insulator as an intermediate layer. However, the thermal surface is subject to a direct exposure to hot air or heat from a heater when activating the thermal adhesive, and, thus, becomes colored. Also, a heater for providing thermal energy in order to activate the thermal adhesive tends to have a high temperature, so that the safety of the process can be compromised. Also, the easy handling of the thermal-recording labels can be diminished. Thus, the above-described methods are not preferable for practical purposes.
Accordingly, there is a need in the field of the thermal-recording labels for a thermal-recording label having no peeling sheet but a thermal adhesive layer which includes an infrared absorption substance and can be activated from a non-adhesive state to a adhesive state through a light to heat conversion, without compromising safety and without bringing about coloring on the thermal surface.